The safe way to the hotel it's and official taxi(u will see them at the entry of the airport).Las Mercedes it's one of the safer areas in Caracas.
I agree with people in here that Caracas it's the more dangerous place in Venezuela but i never had a problem there(and next summer will be the 8th time i go there).I have even go party at night in,Las Mercedes(Caracas),El Tigre,and Puerto Ordaz.
For sure u must be careful as u must do it in all latin america.
Maybe it's because that i'm spanish that i think like that but,really never a single problem there.Don't show u have money at the streets,and don't go to the "cerros"(shantitowns).And that's all.